The present invention relates generally to flight simulators, and more particularly to an improvement in wrap-around display systems for presenting out-the-window visual imagery in a flight simulator.
A critical requirement for realistic flight simulation is that the video display provide a complete field-of-regard (the range of views available to a pilot from an aircraft cockpit by moving about his or her head). Other important requirements include a wide instantaneous field-of-view (the range of views available to a pilot at any instant while holding still his or her head), high contrast and high resolution. All of these requirements should be obtained, of course, with a compact structure and at low cost.
The prior art has provided wide field-of-regard and wide field-of-view display systems generally by the use of large domes (12 to 20 feet in radius) with multiple video projectors mounted inside the dome. The large radius has been considered necessary to provide a so-called infinity display in which the light from the virtual image to the eyes of a flight simulator pilot was collimated so that it would appear to be focused at infinity. It has been believed that an infinity display is necessary for the image to appear sufficiently real to the simulator pilot to make a successful simulation. In addition to their high cost, these large dome systems suffer from an inherent problem in positioning the projectors. The ideal location for both the projectors and the design eye-point (the point inside the simulator where the simulator pilot's eyes are expected to be located) is the center of the dome. Moving the projectors from this ideal location forces undesirable compromises on display brightness and illumination evenness. It is also very difficult to position the projectors and their associated correction optics to provide a sufficient field-of-regard approximating that of a modern fighter aircraft. Another critical problem with such dome display systems is that the internally reflective domes are spherical integrators in that the projected light makes multiple bounces inside the dome resulting in a high level of ambient illumination. This markedly reduces the resulting contrast ratio in the originally projected screen, typically resulting in contrast ratios less than 10:1.
A modification of such prior art dome systems is described in U.S. Pat. No. 4,473,355 to Pongratz. The Pongratz patent describes a dome display in which a plurality of rear projectors mounted outside a translucent dome project the image back toward the dome. The inside of the dome is covered with a Fresnel lens system in which a plurality of Fresnel lens each have their optical axis directed toward the cockpit inside the dome so that an infinity display is provided.
Another approach is described in U.S. Pat. No. 3,514,871 to Tucker. The Tucker patent describes a wrap-around visual display system made with three horizontally arranged rectangular rear-projection screens positioned at angles to each other to roughly wrap-around the front of the simulator pilot. The screens are spaced five or more feet from the simulator pilot. Three large convex lens are positioned one each in-between the simulator pilot and the rear-projection screens. The lens are to give the simulator pilot the impression that the virtual images are focused at infinity.
A further approach for making an infinity display is described in U.S. Pat. No. 4,391,495 to Mazurkewitz. The Mazurkewitz patent describes a screen comprising a plurality of Fresnel lens positioned in-between the eyes of a viewer and a cathode ray tube (CRT) display. The Fresnel lens arrangement has a large exit pupil so that the viewer has more freedom of head movement (typically side-to-side) before the visually corrected image is lost. The Mazurkewitz patent also suggests making a simulator display system of pentagon shaped screens, each made according to the teachings of the Mazurkewitz patent, connected together at their edges to make a 12-sided dodecahedron surrounding the viewer.
The Pongratz, Tucker and Mazurkewitz patents each have as a primary object making a more compact simulator display system while still providing ah infinity display. To achieve this infinity display effect, they must each compromise various combinations of wide field-of-regard, wide field-of-view, resolution, brightness, contrast and low cost.
A more recently developed display system for flight simulators is the Fiber Optic Helmet Mounted Display (FOHMD) developed by CAE Electronics in Montreal, Canada. This display has excellent brightness, contrast and resolution, but is nearly as expensive as a dome and cannot deliver a wide instantaneous field-of-view. It also requires an extensive set of optics mounted on a custom helmet which detracts from the simulator pilot's ability to make natural head motions. The helmet optics also act as dark sunglasses, allowing only about ten to twenty percent of the ambient light to filter through, thus making it very difficult to provide sufficient cockpit illumination for instrument viewing and map reading.
Thus it is seen that there is a nee for a compact visual display system for flight simulators that combines compactness with wide field-of-regard, wide field-of-view, resolution, brightness, contrast and low cost.
It is, therefore, a principal object of the present invention to provide a compact, cost effective, out-the-window visual display system for flight simulators that has a wide field-of-regard, wide field-of-view, reasonable resolution, and high brightness and contrast.
It is another object of the present invention to provide a display system for flight simulators that can display separate geometrically correct displays for each of a pair of simulator crewmembers sitting in different positions inside a flight simulator.
It is a feature of the present invention that it can simulate a multi-channel display of more video channel signals than are actually continuously available in the system.
It is an advantage of the present invention that it is very cost effective and straightforward to manufacture because it is made largely with relatively low-cost, off-the-shelf components.
These and other objects, features and advantages of the present invention will become apparent as the description of certain representative embodiments proceeds.